21171823 has 2 divisors, whose sum is σ = 21171824. Its totient is φ = 21171822.

The previous prime is 21171811. The next prime is 21171841. The reversal of 21171823 is 32817112.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21171823 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21171883) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10585911 + 10585912.

It is an arithmetic number, because the mean of its divisors is an integer number (10585912).

Almost surely, 2^21171823 is an apocalyptic number.

21171823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21171823 is an equidigital number, since it uses as much as digits as its factorization.

21171823 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 672, while the sum is 25.

The square root of 21171823 is about 4601.2849292344. The cubic root of 21171823 is about 276.6428296748.

Adding to 21171823 its reverse (32817112), we get a palindrome (53988935).

The spelling of 21171823 in words is "twenty-one million, one hundred seventy-one thousand, eight hundred twenty-three".